FIGS. 1A-1D are plan views illustrating a method of manufacturing a photovoltaic device disclosed in Japanese Patent Laying-Open No. 62-76786.
Referring to FIG. 1A, a plurality of first electrodes 3a, 3b and 3c are formed respectively on a plurality of cell areas 2a, 2b and 2c on an insulator substrate 1 of rectangular shape. The first electrodes 3a, 3b and 3c have first extended portions 3ae, 3be and 3ce for an electrical connection, respectively, along the bottom side of the substrate 1.
Referring to FIG. 1B, the first electrodes 3a, 3b and 3c are covered with a photo-active semiconductor layer 4. The semiconductor layer 4 includes a pn junction or a pin junction, parallel to the first electrodes 3a, 3b and 3c.
Referring to FIG. 1C, an energy beam such as a laser beam or an electron beam is directed onto the semiconductor layer 4 along the bottom side of the substrate to irradiate the layer 4, thereby forming a groove 4a penetrating the semiconductor layer 4. The groove 4a runs across each of the first extended portions 3ae, 3be, and 3ce. That is, a portion of each of the first extended portions 3ae, 3be and 3ce is exposed within the groove 4a.
Referring to FIG. 1D, a plurality of second electrodes 5a, 5b and 5c are formed on the semiconductor layer 4, respectively in the plurality of cell areas 2a, 2b and 2c. The second electrodes 5a, 5b and 5c have second extended portions 5ae, 5be and 5ce for an electrical connection, respectively, along the bottom side of the substrate 1. Further, a lead-out electrode 6 is formed on the semiconductor layer 4 so as to overlap the first extended portion 3ae of the first electrode 3a at the left end of the rectangular substrate.
As a result, the lead-out electrode 6 is connected through the groove 4a to the first extended portion 3ae of the first electrode 3a at the left end. Further, the second extended portion 5ae of the second electrode 5a at the left end is connected through the groove 4a to the first extended portion 3be of the first electrode 3b at the center of the substrate. Similarly, the second extended portion 5be of the second electrode 5b at the center is connected to the first extended portion 3ce of the first electrodes 3c at the right end of the substrate. That is, such a photovoltaic device is formed so that three photovoltaic cells in the respective cell areas 2a, 2b and 2c are connected in series to one another.
When light enters from the substrate side into the photo-active semiconductor layer 4, the first electrodes 3a, 3b and 3c made of a transparent conductive oxide (TCO) are formed on the transparent insulator substrate 1. On the other hand, when light enters from the opposite side into the semiconductor layer 4, the second electrodes 5a, 5b and 5c are formed of the TCO.
In the described method of manufacturing the photovoltaic device of the prior art, when the groove 4a is formed by an energy beam, there is a danger that particles of the semiconductor scatter and then remain on the semiconductor layer 4. The semiconductor particles sandwiched between the semiconductor layer 4 and the second electrodes 5a, 5b and 5c exert an adverse effect on the characteristics of the photovoltaic device.
Further, the semiconductor layer 4 is exposed to its surroundings for a long period of time, in the step of forming the groove 4a by the laser beam. Consequently, there is a danger that the surface of the semiconductor layer 4 is oxidized, absorbs water or is contaminated by dust, fats and oils or the like. The resultant oxide film, water, contamination and the like on the surface of the semiconductor layer 4 have an adverse effect not only on the electric characteristics of the photovoltaic device but also on the electrical contact between the second electrodes 5a, 5b and 5c and the semiconductor layer 4.
Moreover, since the respective first extended portions 3ae, 3be and 3ce of the first electrodes 3a, 3b and 3c are exposed in the formed groove 4a, those exposed portions are liable to be contaminated before formation of the second electrodes 5a, 5b and 5c.